نتایج جستجو برای: overdispersion

تعداد نتایج: 555  

2012
Wondwosen Kassahun Thomas Neyens Geert Molenberghs Christel Faes Geert Verbeke

UNLABELLED BACKGROUND In medical and biomedical areas, binary and binomial outcomes are very common. Such data are often collected longitudinally from a given subject repeatedly overtime, which result in clustering of the observations within subjects, leading to correlation, on the one hand. The repeated binary outcomes from a given subject, on the other hand, constitute a binomial outcome, ...

Journal: :Computational Statistics & Data Analysis 2009
Amparo Baíllo J. R. Berrendero Javier Cárcamo

A new methodology to detect zero-inflation and overdispersion is proposed, based on the comparison of the expected sample extremes among convexly ordered distributions. The method is very flexible and includes tests for the proportion of structural zeros in zero-inflated models, tests to distinguish between two ordered parametric families and a new general test to detect overdispersion. The per...

Journal: :Biometrics 1999
J K Lindsey

Response surface methodology, originally developed for determining optimal conditions in industrial experiments, was early adapted to experiments in marine ecology. However, these involved studying the shape of the complete response surface, not only detecting the optimum, and often had counts or durations as the response variable. Thus, nonlinear, nonnormal response models were required. For c...

Journal: :Statistics in medicine 2012
Tonglin Zhang Zuoyi Zhang Ge Lin

The spatial scan statistic has been widely used in spatial disease surveillance and spatial cluster detection for more than a decade. However, overdispersion often presents in real-world data, causing not only violation of the Poisson assumption but also excessive type I errors or false alarms. In order to account for overdispersion, we extend the Poisson-based spatial scan test to a quasi-Pois...

2009
Willem Albers W. Albers

An attractive way to control attribute data from high quality processes is to wait till r ≥ 1 failures have occurred. The choice of r in such negative binomial charts is dictated by how much the failure rate is supposed to change during Outof-Control. However, these results have been derived for the case of homogeneous data. Especially in health care monitoring, (groups of) patients will often ...

Journal: :Genetics 1997
H Araki H Tachida

Variances of evolutionary rates among lineages in some proteins are larger than those expected from simple Poisson processes. This phenomenon is called overdispersion of the molecular clock. If population size N is constant, the overdispersion is observed only in a limited range of 2N sigma under the nearly neutral mutation model, where sigma represents the standard deviation of selection coeff...

Journal: :Lifetime data analysis 2007
Geert Molenberghs Geert Verbeke Clarice G B Demétrio

Non-Gaussian outcomes are often modeled using members of the so-called exponential family. The Poisson model for count data falls within this tradition. The family in general, and the Poisson model in particular, are at the same time convenient since mathematically elegant, but in need of extension since often somewhat restrictive. Two of the main rationales for existing extensions are (1) the ...

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